Selective catalytic reduction (SCR) systems are sometimes employed with compression-ignition engines to reduce nitrogen oxides in the exhaust stream. SCR systems require the use of a reductant, such as anhydrous ammonia, aqueous ammonia, or urea in the exhaust stream. In some systems, diesel fuel is chemically reformulated to create ammonia. Accordingly, when the reductant is not derived from the main fuel of the engine, a separate tank is employed to store the reductant prior to injection of the reductant into the exhaust stream.